1. Technical Field
The present invention relates to an indicator position detecting device including an indicated position detecting sensor of an electromagnetic induction system, and particularly to the control of loop coils formed as the indicated position detecting sensor.
2. Description of the Related Art
A position input device of an electromagnetic induction system has recently been used as an input device for a tablet type PC (personal computer) or the like. The position input device includes a position indicator in the shape of a pen (pen type position indicator) and an indicator position detecting device having an input surface on which pointing operation and the inputting of characters, figures, and the like are performed using the pen type position indicator. The pen type position indicator has a resonance circuit including a coil and a capacitor. On the other hand, the indicator position detecting device has an indicated position detecting sensor (position detecting coils), in which an X-axis direction loop coil group formed by disposing a plurality of loop coils in a horizontal direction (X-axis direction) and a Y-axis direction loop coil group formed by disposing a plurality of loop coils in a vertical direction (Y-axis direction) are laminated.
As an example of detecting a position indicated by the pen type position indicator on the indicator position detecting device, one loop coil is selected from the plurality of loop coils forming the indicated position detecting sensor in predetermined order, and a transmission signal is sent out from the selected loop coil to the pen type position indicator. The capacitor of the pen type position indicator is thereby charged. Next, the loop coil used for the transmission is connected to a receiving circuit to receive a signal transmitted from the resonance circuit of the pen type position indicator. Such signal transmission and reception is performed while the loop coils are sequentially selected, whereby the position indicated by the pen type position indicator can be detected on the indicator position detecting device.
The detection of the position indicated by the pen type position indicator on the indicator position detecting device is described in more detail as follows. First, (1) in order to detect where the pen type indicator is on the indicated position detecting sensor, a global scan, which sequentially selects all of the loop coils and detects the position indicated by the pen type position indicator, is performed to identify roughly the indicated position on the indicated position detecting sensor. Next, (2) a sector scan, which selects only a predetermined number of loop coils around the roughly identified position in order and performs signal transmission and reception, is performed to identify the position indicated by the pen type position indicator accurately. Thus, the position indicated by the pen type position indicator on the indicated position detecting sensor can be detected. Incidentally, various inventions have been made for the position input device of the electromagnetic induction system, and Japanese Patent Laid-Open No. 2002-244806, for example, describes details of an example of configuration of the position input device and the like.
Such a position input device of the electromagnetic induction system is not only used as an external input device of a personal computer or the like but also used as an input device of a tablet type PC as described above or an input device of a high-functionality portable telephone terminal referred to as a smart phone. In this case, the position input device of the electromagnetic induction system is disposed so as to be superposed on a display element such as an LCD or the like.